1. Field of the Invention
The invention relates to improvements in eccentric rotary valve for flow control.
2. Description of the Prior Art
There have been many different types of spherical plugs used in prior art valves that are constructed for movement into and out of engagement with a seat port forming a wall of a valve chamber. One example of a prior art rotary valve that is used for this purpose is shown on Hans D. Baumann U.S. Pat. No. 3,623,696.
The spherical plug that is disclosed in the aforementioned patent and an arm which extends therefrom are of a solid one-unit construction. The valve plug and arm are rotatable eccentrically in a valve chamber relative to a port seat by means of an actuator shaft mounted in the wall portions of the valve chamber.
As the actuating shaft is rotated in one direction, it rotates the spherical face of the plug eccentrically relative to the seat face of the port seat. When a portion of the plug comes in contact with the seat, the longitudinal axis of the arm commences to bend and this results in the spherical face of the plug being rubbed against the seat as continued rotation of the plug toward its closed valve position occurs.
Additional similar rubbing action as that just described will take place between the spherical contact portion of the plug and the seat of the seat port when the plug is moved along the seat toward its open position.
From the aforementioned description, it can be seen that a high unit load in the form of a rubbing force is applied on a small segment of the seat port during each successive port closing and port opening operation. This rubbing action thus causes or tends to cause extensive wear to occur between the rubbing surfaces of the spherical plug and the surfaces of the seat port. The greatest extent of wear occurs where the segments of the plug and/or seat port portions are first brought into contact with one another as the valve is closed.
As the valve continues to cycle between an open and closed position, this wearing action intensifies and results in uneven wear occurring between the plug and the seat port and results in increased leakage occurring between the plug and the seat port.
Another difficulty that has been encountered with prior art valves of the aforementioned type and as set forth in detail in the Charles Bates U.S. Pat. No. 3,749,358 is that the seats of many of these valves must be properly shimmed in order to effect perfect alignment and sealing. Such a shimming operation is not desirable since it takes a considerable amount of time to continuously assemble and disassemble the valve until a desirable size shim is selected to provide an acceptable seal between the plug and seat port. The shimming operation has been found to be necessary even though expensive machine shop procedures are effected to machine the parts of these valves to precise tolerances in an attempt to eliminate the valve leakage problem.
Another problem encountered with the valves of the aforementioned type is that an undesired, abnormally high torque is required to close such valves since the plug arm, that extends between the back of the plug and the actuator shaft, is required to be flexed as the aforementioned rubbing action occurs between the plug and its seat port. Use of such one-unit plug-arm construction will, therefore, require an expensive, rather large size actuator to effect the opening and closing of such rotary valves.
Another difficulty in the use of the aforementioned prior art rotary valve is that the entire valve, including the actuator shaft, arm and plug must be completely removed as a single unit from its assembled position in the valve chamber in order to replace a defective plug with a new one. Replacement is then accomplished by sliding the arm and plug unit off one end of the actuating shaft and slidably mounting a new unit on the shaft.
For the aforementioned reasons, a substantial amount of down time in a process being controlled by the aforementioned rotary valve will be required when replacing a defective plug with a new one.